A Glock 40 and a CCW should be sufficient. No need for a shotgun, unless you want to pull it out afterward for good measure.
Look, I’m trying to get helpful information out there, based on my personal experience and the experiences of other pit bull owners. I don’t have a problem with shooting an attacking dog; you could use my advice to get the animal into a position where you could get a clean shot off.
As much as we all love to hear about how you’re going to hit the dog with napalm and then stick your 50 cal up it’s nose, I think my way is a little more practical.